Method of bonding a titanium member to a ceramic surface



1958 P. R. DIJKSTERHUIS ET AL 2,859,512

METHOD OF BONDING A TITANIUM MEMBER TO A CERAMIC SURFACE Filed April 2, 1956 INVENTORS POPKO REINDER KSTERHUIS ALBERTUS REM MOVING AGENT nite States METHUD OF BONDlNG A TITANTUNI MEMBER TO A CERAMIC SURFACE Popko Reinder Dijksterhuis and Albertus Remko Hovingh, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware The invention relates to a method of vacuum-tight fastening of a metal object to a ceramic surface and, more particularly, to an electric discharge tube having at least one supply conductor secured in a vacuum-tight manner to one or more ceramic surfaces.

It is known that titaniumand zirconium-containing alloys adhere satisfactorily to ceramic surfaces, more particularly, of alundem. It is common practice to coat first the ceramic surface with a layer of Ti, to which the metal objects can be soldered. The titanium is applied in the form of TiH and decomposed by heating in a nonoxidizing atmosphere. It is also known that silver solder to which Li, P or Mn is added, is suitable to solder an object to a ceramic surface, the admixtures forming a vitreous compound with the ceramic surface. In order to obtain a satisfactory adhesion, the ceramic surface may be coated previously with oxides of vanadium, niobium or tantalum.

However, all these known methods are comparatively complicated. In accordance with the invention a very simple method of fastening a metal object to a ceramic surface is obtained, if the metal object of titanium or zirconium is brought into contact with the ceramic surface with the interposition of a layer of metal or metal alloy having a lower melting-point than Zr, in which Ti or Zr can dissolve to a small extent, after which the temperature is raised in vacuo to an extent such that the intermediate metal melts and adheres to the ceramic surface owing to the Ti or Zr dissolved in the metal. The heating operation may be continued until such a quantity of Ti or Zr has dissolved in the intermediate metal that the melting-point reaches or exceeds the heating temperature, so that during the heating operation the metal solidifies. Suitable intermediate metals are nickel, iron, cobalt. The ceramic material consists preferably of alumina, since its expansion coefficient corresponds approximately to that of Ti and Zr.

The effect obtained is very likely due to the phenomenon that the Ti or Zr dissolves in the liquid intermediate metal, which need in itself not adhere to the ceramic surface, the dissolved Ti or Zr thus enabling a moistening of the ceramic surface, so that the metal adheres to the ceramic surface. Owing to the solution of Ti or Zr the melting-point of the intermediate metal increases gradually, so that after some time the metal can solidify during the heating operation.

The invention will be described more fully with reference to a drawing, which shows one embodiment of a discharge tube manufactured by carrying out the method according to the invention.

Referring to the figure, reference numeral 1 designates a titanium disc, to which the anode cylinder 5 is secured, 2 designates the titanium disc to which the grid atent O 6 is fastened and the titanium disc 3 supports the cathode 7. One end of the filament wire 8 is secured to the cathode disc 3, the other end of the titanium disc 4.

Between the titanium discs provision is made of ceramic discs 15, 16 and 17, having a height such that the correct distance between the electrodes is obtained, when the parts of the tube are piled upon one another. Between the discs and the ceramic end surfaces of the cylinders provision is made of rings 9, 10, 11, 12, 13 and 14 made for example of Ni, Fe or C0, the thickness of which must be extremely small, for example 5 to 10 ,u, since otherwise too great a quantity of Ti is dissolved in the metal. The melting of these rings does not affect markedly the electrode spacings. The tube is exhausted under a vacuum bell. During the degassing the heating operation may be performed in the conventional manner, for example by means of high-frequency currents. Then the heating of the metal discs 1 to 4 is raised to a temperature such that the rings 9 to 14 melt. A small quantity of Ti then dissolves in the molten metal of the rings 9 to 14 and produces a moistening of the ceramic surfaces with this metal, so that a satisfactory adhesion is obtained. At the same time the melting temperature of the liquid metal increases, so that during the heating operation this metal can solidify. The hot Tior Zi-discs operate in this case at the same time as a getter, so that a satisfactory vacuum is obtained in the tube, after the parts of the tube have been soldered to one another. Subsequent to cooling the tube may be removed from the bell. The method according to the invention is particularly suitable for the manufacture of tubes for very short waves. A tube as shown in the figure may have a diameter of about 10 mms. and a height of for example 12 mms. These dimensions may, however, be chosen greater or smaller in accordance with need without causing difficulties in the establishment of the joints according to the invention.

Although only a single embodiment is described above, it is obvious that the connection of titanium or zirconium the ceramic material with the interposition of one of the said metals or alloys with a lower melting-point may have any shape within the scope of the invention.

What is claimed is:

A method of securing a metal object to a ceramic surface in a vacuum comprising placing between said metal object constituted of titanium and said ceramic surface a metal layer of a thickness between 5n and 10 4 selected from the group consisting of nickel, iron and cobalt in which titanium is soluble to a small extent, said metal layer abutting both said titanium and ceramic surface, heating the assembly in a vacuum to a constant temperature above the melting point of said metal layer but below the melting point of titanium whereby said metal layer dissolves titanium from the abutting surface thereof to form an intermediate alloy therewith which wets and bonds titanium and the ceramic surface to join the same.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,117 Hobrock Apr. 10, 1945 2,627,110 Hickey Feb. 3, 1953 2,713,196 Brown July 19, 1955 2,728,425 Day Dec. 27, 1955 2,739,375 Coxe Mar. 27, 1956 2,770,033 Zarth Nov. 3, 1956 2,800,711 Oliphant et a1 July 30, 1957 

